A sign assembly of this kind is described in U.S. Pat. No. 4,542,605 (Gandy) issued 24 Sept. 1985, the contents of which are hereby incorporated herein by reference. In this prior patent, the flexible sign sheet is tensioned across the frame by a series of separate tensioning devices spaced around the frame, each tensioning device comprising a screw which can be adjusted to increase the tension of the sign sheet across the frame. Although this arrangement provides an effective tensioning procedure, there is currently a need for a simplified procedure.